1. Field of the Invention
The invention relates to new compositions comprising aromatic polyimides containing terminally unsaturated ester groups. More specifically, it relates to such compositions in which the terminal ester groups are moieties that contain terminal CH.sub.2 .dbd.CH-- functions capable of polymerizing and forming crosslinked polymers. Still more specifically, it relates to such polyimide esters and to the crosslinked polymers obtained therefrom without the formation of by-products.
2. State of the Prior Art
Polyimides, as prepared from aromatic dianhydrides and aromatic diamines, are known to have the desired property of high heat resistance and high solvent resistance. Such, polyimides, upon condensation to an infusible condition, generate by-products such as water and other vapors or gases, which introduce voids into the fabricated products that detract from the expected good physical properties. In addition, because of these same desirable properties, they are untractable and therefore very difficult and expensive to work into desired shapes and forms.
Recent patents, such as U.S. Pat. Nos. 3,879,395 and 3,998,786, are directed to improving the tractability of the aromatic polyimides by attaching various terminal groups to polyimide oligomers whereby the chains are extended by coupling of the terminal groups. In both of these patents the coupling groups are attached as terminal imide moieties containing vinyl, propargyl, nitrile, etc. groups. Thus the terminal anhydride group is converted to an imide group containing a vinyl, nitrile, propargyl, etc. group. However, in neither of these patents nor in any other related prior art references, has there been found any reference or disclosure that the terminal anhydride group on each end could be converted to two ester groups of which at least one or both could contain polymerizable groups. Such ester groups would contribute higher tractability to the composition, and the crosslinking groups could be controlled to two, three or four such groups.